It consists of two binary pairs in mutual orbit designated α¹ Herculis or α Herculis A (the brightest of the two) and α² Herculis or α Herculis B.[12][13] A's two components are themselves designated α Herculis Aa (also named Rasalgethi[14]) and Ab; B's as α Herculis Ba and Bb.

Alpha Herculis also forms the A and B components of a wider system designated WDS J17146+1423 with two additional visual companions designated WDS J17146+1423C and D.[15]

Alpha Herculis bore the traditional name Rasalgethi or Ras Algethi (Arabic: رأس الجاثي ra‘is al-jāthī‎ 'Head of the Kneeler').[17] 'Head' comes from the fact that in antiquity Hercules was depicted upside down on maps of the constellation. In 2016, the IAU organized a Working Group on Star Names (WGSN)[18] to catalog and standardize proper names for stars. The WGSN approved the name Rasalgethi for the component Alpha Herculis Aa on 30 June 2016 and it is now so included in the List of IAU-approved Star Names.[14]

The term ra's al-jaθiyy or Ras al Djathi appeared in the catalogue of stars in the Calendarium of Al Achsasi al Mouakket, which was translated into Latin as Caput Ingeniculi.[19]

Alpha Herculis A and B are more than 500 AU apart, with an estimated orbital period of approximately 3600 years. A presents as a relatively massive red bright giant, but radial velocity measurements suggest a companion with a period of the order of a decade.[15] B's two components are a primary yellow giant star and a secondary, yellow-white dwarf star in a 51.578 day orbit.

Alpha Herculis Aa is an asymptotic giant branch (AGB) star, a luminous red giant that has both hydrogen and helium shells around a degenerate carbon-oxygen core. It is the second nearest AGB star to the Sun.[3] The angular diameter of the star has been measured with an interferometer as
34 ± 0.8 mas, or 0.034 arcseconds.[22] At its estimated distance of 110 parsecs this corresponds to a radius of about 280 million kilometers (or 170 million miles), which is roughly 400 R☉ or 1.87 AU.[23] If Rasalgethi were at the center of the Solar System its radius would extend past the orbit of Mars at 1.5 AU but not quite as far as the asteroid belt. The red giant is estimated to have started its life with about 2.175-3.250 M☉.[3]

Like most type M stars near the end of their lives, Rasalgethi is experiencing a high degree of stellar mass loss creating a sparse, gaseous envelope that extends at least 90 AU.[24] It is a semiregular variable with complex changes in brightness with periods ranging from a few weeks to many years. The most noticeable variations occur at timescales of 80–140 days and at 1,000 - 3,000 days. The strongest detectable period is 128 days.[25] The full range in brightness is from magnitude 2.7 to 4.0,[2] but it usually varies over a much smaller range of around 0.6 magnitudes.[25]

where δ equals Rasalgethi's angular diameter in arcseconds, dR the star's diameter in AU, and DR the Distance from Earth in parsecs. If one knows the angular diameter and the Distance, then one can solve for dR as follows: